[Dart] Add UInt8List support, allowing for type:string format:binary definitions

Created by: 0xNF

Summary

tl;dr UInt8List support, which Dart-Dio has, has been added to the regular Dart2 generator.

Fixes #12161.

Details

Changes to the Generators:

To support UInt8List in the generator, Typed Data imports had to be added. Additionally, some OpenAPI data types have been switched to Uint8List.

• [AbstractDartCodeGen.java]: added Uint8List/dart:typed_data to the imports.
• [AbstractDartCodeGen.java]: Changed typeMapping of {file, binary} to Uint8List away from MultiPartFile
• [AbstractDartCodeGen.java]: Copied Multipart/Uint8list differentiation in postProcessOperationsWithModels from DartDioClientCodegen.java
• [dart2/apilib.mustache]: Added import 'dart:typed_data';

Changes to the API classes

To support Uint8List in the generated API output, parts of the *api.dart files had to be refactored. Presently Dart2 relies on passing utf8 decoded response byte strings through its API calls, but this leads to errors because not all response objects are json strings. To handle this, I refactored many of the calls to take Uint8List's straight from response.bodyBytes. Decoding into a String object doesn't happen until it needs to, which is right before passing the object down into the Json Decoding section.

• [api_client.dart]: deserialize and deserializeAsync now take Uint8List as their default input
• [api_helper.dart]: removed _decodeBodyBytes in favor of just using response.bodyBytes
• [api_helper.dart]: added decodeError method to deal with the byte response, which decodes the resposne into a utf-8 String.

To confirm this change, use the following specfile:

specfile

openapi: 3.0.3
info:
  version: "1.1"
  title: Dart Uint8list Demo
servers:
  - url: "localhost"
    variables:
      host:
        default: localhost
paths:
  /getData:
    get:
      operationId: GetData
      description: "Should return a Uint8List of bytes"
      responses:
        "200":
          description: Binary data
          content:
            application/octet-stream:
              schema:
                type: string
                format: binary
    put:
      operationId: PutData
      description: "Should push a Multipart File"
      requestBody:
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                fileContent:
                  type: string
                  format: binary
      responses:
        "200":
          description: OK
          content:
            application/json:
              schema:
                type: string
  /item:
    get:
      operationId: GetItem
      description: "Should return an Item"
      responses:
        "200":
          description: items
          content:
            application/json:
              schema:
                $ref: "#components/schemas/item"
components:
  schemas:
    Item:
      type: object
      description: "Some json thing"
      required:
        - intField
        - doubleField
        - stringField
        - dateField
        - timeField
        - dateTimeField
        - boolField
        - b64Field
        - intArrayField
      properties:
        intField:
          type: integer
          format: int32
        doubleField:
          type: number
          format: float
        stringField:
          type: string
        dateField:
          type: string
          format: date
        timeField:
          type: string
          format: time
        dateTimeField:
          type: string
          format: date-time
        boolField:
          type: boolean
        b64Field:
          type: string
          format: byte
        intArrayField:
          type: array
          items:
            type: integer
            format: int32

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